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8/12/2019 Mei Wirebonder Brief Operations Guide
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MEI Wire Bonder Brief Operation Guide
1 Basics of the Bonding Process.................................................................................... 2
2 Instrument Operation .................................................................................................. 42.1 Sample Mounting................................................................................................ 4
2.2 Setting Bonding Parameters................................................................................ 4
2.2.1 Bonding Weights: ....................................................................................... 4
2.2.2 Bonding Heights: ........................................................................................ 52.3 Manual Operation using the Z-arm control ........................................................ 5
2.3.1 The Bonding Cycle ..................................................................................... 5
2.3.2 First Bond (Ball Bond, Channel 1) ............................................................. 52.3.3 Second Bond (Stitch Bond, Channel 2) ...................................................... 6
2.4 Issues That Effect Bonding Performance ........................................................... 6
2.4.1 Free air ball (FAB)...................................................................................... 62.4.2 Adjustments to Change Free Air Ball Size ................................................. 7
2.4.3 First Height Adjustment.............................................................................. 8
2.4.4 Second Height Adjustment ......................................................................... 9
2.4.5 Changing the Capillary ............................................................................. 102.4.6 Parameters needed for semi-automatic bonding (using the silver cycle
button on the micropositioner.)................................................................................. 11
3 MEI Bond Parameter Sheet ...................................................................................... 15
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1 Basics of the Bonding ProcessThermosonic tailless ball and stitch bonding is the most widely used assembly techniquein the semiconductors to interconnect the internal circuitry of the die in the external
world. This method is commonly called, Wire Bonding. It uses force, power, time,
temperature, and ultrasonic energy (sometimes referred to as bonding parameters) to formboth the ball and stitch bonds.
Ball bond formation Stitch bond formation
The ultrasonic transducer (typically for newgeneration of wire bonders, the piezoelectric
element is >100KHz), which converts the
electrical energy into mechanical energy,transmits this resonant energy at the tip of the
bonding capillary. The capillary that is clamped
perpendicularly to the axis of the transducer-
tapered horn is usually driven in a y-axis direction
vibration mode.
Bonding capillaries are made of high-density Alumina ceramic material, Al2O3,
typically 1/16" (.0625" / 1.587mm) in diameter and .437" (11.10mm) in length. The finalcapillary design depends upon the package/ device application and wire diameter to be
used. To determine the correct capillary design in general, bond pad pitch (BPP), bond
pad opening (BPO), target mashed ball diameter (MBD) are the essentials.
Variation characteristic of the
capillary
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A fine gold wire made of soft, face-
centered-cubic metal (FCC),usually ranging from 18m to
33m in diameter (depending upon
the device/ package application) is
fed down through the capillary. It isusually characterized by its
elongation (shear strain), and
tensile strength (breaking load).Selection of the appropriate wire
type to be used for a given
application would be dependent onthe specification of these
elongation, and tensile strength. In
general, the higher elongation (or
higher strain), it means that the
wire is more ductile. This is a goodchoice for low-loop, and short wire
type of wire bonding application. Ifthe requirement is for higher pull
strength readings, a harder wire
type having a higher tensile strength has to be considered.
The small incursions of ultrasonic energy at the tip of the capillary are transmitted to the
Au ball and down to the Al bond pad to form the ball bond. After which, the capillarylifts up and form the looping profile, and then comes down to form the stitch bond. This
cycle is repeated until the next unit is bonded.
If the pad is of a different metal other than Au. Anintermetallic compound, Au-Al, is formed when
the Au is bonded thermosonically to the Al bond
pad metallization. The metallurgical interface ofvoid free Au-Al formation has a significant
increase in the shear strength readings of the ball
bonds tested- provided that there are no impuritiespresent in the bond interface even if it has been
exposed to high temperatures. However, if the
impurities are in the interface are welded poorly,
the ball shear strength produces a significantdegradation in its readings.
Formation of intermetallic compound
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2 Instrument Operation
Assuming that the loop and reset heights are in the appropriate positions the basic manualoperation of the wire bonder goes as follows.
2.1 Sample Mounting
Mount your sample on the work holder and clamp it, then set the height of the surfaceto be bonded according to the work height standard. This can be done by loosening
the set screw on the side of the work holder and adjusting the hex screw on the
underside of the work holder (see Figure 1). Keep in mind the stage can be heated
and will be hot when you go to unload your sample.
Figure 1 Setting the workstage height
2.2 Setting Bonding Parameters
Turn on the bonder and the heated stage. Check the bonding parameters (power and
time on channels 1 and 2, first and second weights) Use recommended starting
parameters.Example Parameters: Ball Bonding 50nm sputtered Au on Channel 1: Power: 6
Time: 4 Dual Weight: 7.
Bonding Au emulsion layer on PCB board on Channel 2: Power: 6.7 Time: 7
Bond Force: 8.5 Heated stage: 80 C
2.2.1 Bonding Weights:
Manual Recommends 35 to 50 grams for Dual Weight for 1 mil wire. With theinstrument calibrated: the 0-14 range on the Dual Weight dial goes from 10 to
110 grams this is the bond forcefor Channel 1 (first bond).The Bond Force
dial 0-14 ranges from 60 to 150 grams when calibrated this is for Channel 2
(second bond). (see end of this guide for calibration routine) (Calibrated and
dials reset 1_22_08)
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2.2.2 Bonding Heights:
If the work height standard was used a value of for Loop Height and for Reset
Height should work. It is important that the Reset Height is high enough so the
EFO wand clears sample when firing. See towards the end of this guide for
adjusting the values.
2.3 Manual Operation using the Z-arm control
The Z arm lets the operator have direct control of the up and down motion of the
machine during the bonding process (see figure 2 for bonding process). The Z-arm
gives the operator multi-level bonding capabilities for more complex applications
without changing any settings on the machine. The Z-arm is located on the lowerright side of the machine. Do not cycle the EFO with the Z-arm depressed
2.3.1 The Bonding Cycle
Figure 2 Bonding Cycle
2.3.2 First Bond (Ball Bond, Channel 1)
After properly loading the sample on the work holder and setting the height, place thework holder on the stage and look through the microscope to position the part to
make the first bond using the micro positioner. Lower the Z-arm until the bonding
Channel 1
Channel 2
Channel 2
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tool contacts the part. Continue down with the Z-arm to cycle the machine. Once the
ultrasonics have fired, raise the Z-arm.
2.3.3 Second Bond (Stitch Bond, Channel 2)
Move the part to make the second bond, using the micropositioner. Lower the Z-armagain, which will trigger the ultrasonics at the end of its stroke.
The Z-arm triggers the logic on the machine by using photocells located in the bottom
of the machine.
The operator should not use much force to move the Z-arm. Bond head speed is
controlled by the damper, and is independent of the speed the Z-arm is moved. Thisprovides a uniform force for bonding.
2.4 Issues That Effect Bonding Performance
2.4.1 Free air ball (FAB).
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2.4.2 Adjustments to Change Free Air Ball Size
Figure 3 Wire bonder components
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2.4.3 First Height Adjustment
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2.4.4 Second Height Adjustment
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2.4.5 Changing the Capil lary
Figure 4 MEI Transducer Side View
If the capillary appears damaged and or the shape of the top of the ball bond appears
inconsistent the capillary may need to be changed. In transducer, place appropriatecapillary for wire size to be bonded. Note: Top of capillary should be flush with the top
of transducer. Secure capillary by tightening cap screw using tool height gauge to set
height.
The wire feeds off the bottom of the spool and threads between the looping drum and
guide wire then straight through the wire guide (about the clamps) between the clamppads and through the capillary.(Fig 4)
NOTE: After threading the machine, pull the wire through the capillary and check thatthe wire feeds smoothly through the guides and off the spool.
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2.4.6 Parameters needed for semi-automatic bonding (using thesilver cycle button on the micropositioner.)
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3 MEI Bond Parameter Sheet
BallBond (1st weight)
StichBond
(2ndweight) Comments
Name Date? Mat? Thick? Power TimeDual
Weight Power Time
Bond
Force
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MEI Bond Parameter Sheet
Ball
Bond (1st weight)
Stich
Bond (2ndweight) CommentsName Date? Mat? Thick? Power Time
DualWeight Power Time
BondForce
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MEI Bond Parameter Sheet
Ball
Bond (1st weight)
Stich
Bond (2ndweight) CommentsName Date? Mat? Thick? Power Time
DualWeight Power Time
BondForce
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